Is it reasonable to compare outputs between JMH and hprof?

[Xuelei Fan]

> These are calls with SHA (i.e. SHA1) or SHA2 in the stack
> (depth=4), and time for SHA2 vs SHA1 is 45.38% vs 1.09%.

Where is the other 98.91% cost for SHA1?  You only call message digest
in the test, instinctively, shall most of the resources are cost by the
message digest, directly or indirectly?

Xuelei


On 12/4/2014 12:09 PM, Wang Weijun wrote:
> Hi All
> 
> I am comparing the difference of SHA-1 and SHA-256. First I wrote a JMH benchmark:
> 
> @Benchmark
> public void sig1(Blackhole bh) throws Exception {
>     bh.consume(sig("SHA-1"));
> }
> 
> @Benchmark
> public void sig2(Blackhole bh) throws Exception {
>     bh.consume(sig("SHA-256"));
> }
> 
> byte[] sig(String alg) throws Exception {
>     MessageDigest md = MessageDigest.getInstance(alg);
>     md.update(new byte[10000]);
>     return md.digest();
> }
> 
> The output is
> 
> Benchmark            Mode  Samples      Score      Error  Units
> o.o.b.Weird.sig1    thrpt        5  20984.435 ± 3356.455  ops/s
> o.o.b.Weird.sig2    thrpt        5  13130.330 ±  976.824  ops/s
> 
> so the difference is there but not huge.
> 
> Then I wrote a simple app with
> 
> public static void main(String args[]) throws Exception {
>     int i = Arrays.hashCode(sig("SHA-1"));
>     i += Arrays.hashCode(sig("SHA-256"));
>     System.out.println(i);
> }
> 
> static byte[] sig(String alg) throws Exception {
>     MessageDigest md = MessageDigest.getInstance(alg);
>     md.update(new byte[10000]);
>     return md.digest();
> }
> 
> and then profile it with -agentlib:hprof=cpu=times, and get
> 
> SHA2    1 10.16% 10.16%     156 303276 sun.security.provider.SHA2.implCompress
> SHA2    2  6.91% 17.07%    9984 303274 sun.security.provider.SHA2.lf_sigma0
> SHA2    3  5.28% 22.36%    9984 303271 sun.security.provider.SHA2.lf_sigma1
> SHA2    4  4.61% 26.96%    7488 303269 sun.security.provider.SHA2.lf_delta0
> SHA2    5  4.20% 31.17%   29952 303273 sun.security.provider.SHA2.lf_S
> SHA2    7  3.79% 39.16%    7488 303266 sun.security.provider.SHA2.lf_delta1
> SHA2    9  2.85% 44.99%   29952 303270 sun.security.provider.SHA2.lf_S
> SHA2   13  1.90% 54.47%   14976 303267 sun.security.provider.SHA2.lf_S
> SHA2   17  1.49% 61.25%   14976 303264 sun.security.provider.SHA2.lf_S
> SHA2   22  0.81% 66.12%    7488 303265 sun.security.provider.SHA2.lf_R
> SHA2   23  0.81% 66.94%    9984 303275 sun.security.provider.SHA2.lf_maj
> SHA2   25  0.81% 68.56%     156 303263 sun.security.provider.ByteArrayAccess.b2iBig64
> SHA2   27  0.68% 70.05%    9984 303272 sun.security.provider.SHA2.lf_ch
> SHA2   31  0.54% 72.63%    7488 303268 sun.security.provider.SHA2.lf_R
> SHA1   34  0.54% 74.25%     156 303224 sun.security.provider.SHA.implCompress
> SHA1   43  0.41% 78.05%     156 303223 sun.security.provider.ByteArrayAccess.b2iBig64
> SHA2   60  0.27% 82.66%    2496 303262 java.lang.Integer.reverseBytes
> SHA2   61  0.27% 82.93%      64 303290 sun.security.provider.SHA2.lf_sigma1
> SHA1  116  0.14% 91.06%    2496 303222 java.lang.Integer.reverseBytes
> 
> These are calls with SHA (i.e. SHA1) or SHA2 in the stack (depth=4), and time for SHA2 vs SHA1 is 45.38% vs 1.09%. With such a small app I don't think SHA or SHA2 is called anywhere else. This is jdk9 b40.
> 
> Why is the output so different from JMH? Is it reasonable comparing them?
> 
> Thanks
> Max
>